The application relates to a method and an apparatus for monitoring tools for breakage and wear without contacting them, particularly those tools which can automatically be exchanged in machine tools.
With increasing automatization of numerically controlled machines, it becomes more and more important to be able to automatically monitor these tools, independently of operating personnel. For example, indirect measuring methods are known which monitor by means of mechanical, inductive, capacitive or optical scanning systems and which examine the tool after each processing operation to assure that it is still in good condition. However, these systems have the drawback that they are unable to recognize a sudden total failure of the tool soon enough and thus the consequential damages caused by breakage of the tool can often not be prevented.
A system has been developed for early detection of total failure, or breakage, in ceramic cutting implements where cracks in the ceramic cutting member lead to destruction of a thin conductive path vapor-deposited on the end flank of the implement. The drawbacks here, however, are the high costs involved for the vapor-deposition of conductor paths at each end flank and the attachment of contact points at the tool holder. Furthermore, because of the insulating properties required of the cutting substance, the measuring process is limited to ceramic cutting implements and does not permit the detection of microcracks at a major cutting edge of a tool.
The publication VDI-Z 116 (1974), pages 1427 et seq.--discloses a fiber optic measuring method in which a scanning head equipped with five bands of 25.mu. thick glass fibers is accommodated in a parallel rocker and measures wear in that a rotating eccentric passes it along the flank of a turning tool. Due to the differences in reflection behavior between worn and unworn flanks, a light signal results in a photo voltage whose pulse flank width is a function of the width of the existing wear trace.
But this method is also very inaccurate and cannot stop the machine fast enough if breaks occur very suddenly.